Aedes aegypti ferritin heavy chain homologue: feeding of iron or blood influences message levels, lengths and subunit abundance

Secreted ferritin in the mosquito, Aedes aegypti, has several subunits that are the products of at least two genes, one encoding a homologue of the vertebrate heavy chain (HCH) and the other the light chain homologue (LCH). Here we report the developmental and organ specific pattern of expression of the ferritin HCH messages and of both subunit types in control sugar-fed mosquitoes, in those exposed to high levels of dietary iron, and after blood feeding. When Northern blots were probed with a HCH cDNA, two bands were observed, representing at least two messages of different sizes that result from the choice of two different polyadenylation sites. Either raising mosquito larvae in an iron-enriched medium, or blood feeding adult female mosquitoes resulted in a marked increase in the HCH message level, particularly of the shorter message. Changes in the amount and length of messages and amount of ferritin subunits were studied over the life span of the mosquito and in different organs of female mosquitoes after blood feeding. The midgut of blood-fed insects is the main site of increased ferritin message synthesis. Ferritin protein levels also increase in midgut, fat body and hemolymph after blood feeding. Ferritin messages and subunits are synthesized in the ovaries and ferritin is found in the eggs. These observations are discussed in terms of translational and transcriptional control of ferritin synthesis and are compared to similar events in the regulation of Drosophila melanogaster ferritin.